"Hey, I see that [some role playing issue] is bothering you, and you speak English. [Here] (link) is a good thread about it. You can also check out this web-site, it's full of interesting content about RPGs! It's a Q&A site, but it's not like Yahoo! Answers, really, just trust me, it's not bad! It's more like a good RPG forum, but not a forum, and anyone can ask and answer freely, and you can edit anyone's post like in a wiki, and your posts can be edited... Oh, wait, you don't understand what it is?! Not eager to join?! Why?!"
OK, now seriously: StackExchange is a very special place. It's certainly a good place, but it takes time to understand how it works. It takes effort.
How can I briefly describe RPG.SE to someone I know who is interested in RPGs and speaks English, knows about Q&A sites and forums, but not about the StackExchange culture?